Method and apparatus for operating a water-jet pump

ABSTRACT

A method for operating a water-jet pump, in which the water needed for operation of the pump is recirculated in a cycle. The water is pressurized by means of compressed air at a substantially constant air pressure and the compressed air is used to drive out the water through the water-jet pump. Expanding the compressed air in a defined expansion space withdraws heat from the water by absorbing such heat in the air during and after its expansion. Apparatus for operating a water-jet pump includes a pair of ejecting receptacles and a first water valve for alternate connection of the ejecting receptacles to the pressure side of the water-jet pump. Second water valves return to the ejecting receptacles water which has been discharged from the water-jet pump. A first compressed air valve connects a compressed air source alternately to the ejecting receptacles and a second compressed air valve alternately connects the ejecting receptacles to an expansion vessel for expanding and thereby dropping the pressure of compressed air from the connected one of the ejecting receptacles. Expansion of the compressed air in the expansion vessel cools the water circulated through the water-jet pump, in one embodiment by immersion of the expansion vessel in such water and in another embodiment by spraying of a portion of such water into the expansion vessel.

FIELD OF THE INVENTION

The invention relates to a method for operating a water-jet pump, inwhich the water which is needed for the operation of the pump isrecirculated in a cycle.

BACKGROUND OF THE INVENTION

Water-jet pumps are for example used extensively in laboratories, forexample for drying of substances or for evaporating of solutions at alow temperature, through which a thermal load on the substances to betreated is avoided. Water-jet pumps have the advantage that they arebuilt very simply, practically have no wear and are practicallyinsensitive against corrosion, if they are, as common, manufactured ofglass or of plastic. A moderate vacuum can be produced withoutdifficulties with water-jet pumps in the range of between 100 mm.mercury column and 15 mm. mercury column, which is sufficient for manylaboratory purposes.

Disadvantageous, in comparison with mechanical pumps, for example rotaryslide valve pumps, is the relatively high operating cost, since thewater usage is considerable; a usual consumption value is for example0.8 m³ /h, so that during a ten-hour operation 8 m³ water are used.Aside from cost, such a high water consumption is also undesirable inview of the environmental resources. To avoid the water consumption, onehas already used the above-mentioned method, according to which thewater is recirculated in a cycle. For this, an electrically drivenrecirculating pump is used to place water, which runs off from thewater-jet pump, again under pressure and feed it to the operating waterconnection of the water-jet pump.

The pressure reachable depends strongly on the temperature of theoperating water, since the pressure can never be less than the steampressure of the operating water, which increases with an increase in thetemperature of the operating water. The operating water heats uprelatively quickly in a recirculating system, so that the suctioncapacity of the water-jet pump is less than with a constant supply offresh water. If one still wants to achieve lower temperatures, then theoperating water must be cooled with special cooling devices. In thiscase, a complex apparatus with many electrical connections is theresult.

The purpose of the invention is to provide a method of theabove-mentioned type such that electrical installations are not neededand still a cooling of the operating water is achieved. Through afurther development of the invention an advantageous apparatus forcarrying out the method is also to be created.

SUMMARY OF THE INVENTION

This purpose is attained according to the invention by the water beingpressurized by means of compressed air at a substantially constant airpressure and by the compressed air, which was used for driving water outthrough the water-jet pump, being expanded, i.e. allowed to drop inpressure, in a defined let-down, or expansion, space, wherein heat iswithdrawn from the water, which is absorbed from the air during andafter its expansion.

In place of a recirculating pump, compressed air is used forrecirculating the water. Compressed air connections are generally atevery work station in modern laboratories, so that setting up a specialcompressor is not needed. Inventively, the air does not drop in pressureduring the driving out of the water, so that a constant water pressureexists at all times at the water-jet pump and thus a constant suctionlevel, or rate, exists. When the compressed air has fulfilled itsdriving-out function, it is used inventively to cool the operating waterto be recirculated. The expansion of the air, which after the drivingout is still under high pressure, greatly cools the air. This coolingoff is utilized to withdraw heat from the operating water. One thereforecan maintain, without any special cooling equipment a low temperature ofthe recirculating water and thus is able to achieve a low pump pressure.Furthermore, the cooled operating water can be guided in an auxiliarycycle through cooling traps and can there replace the otherwise neededfresh water. Since both the recirculation of the operating water andalso the cooling off of the operating water are done with compressedair, no electrical equipment is needed. This is particularlyadvantageous for a laboratory, since electrical installations would haveto be protected particularly against wetness.

Above and hereinafter reference is made to water-jet pumps andcompressed air as driving gas. The invention of course includes alsomethods, in which other liquids are utilized instead of water for theoperation of the pump and in which gases other than air are utilized forthe driving of the liquid. Other liquids and gases may be necessary inthe case of special tasks.

The withdrawal of heat from the water can be effected by recirculatingwater around the expansion vessel, for example by arranging it in awater bath in an outer container. A particularly good efficiency isachieved, however, if the expanding air comes directly into contact withthe water to be cooled, which can be achieved easily by introducingwater through a nozzle into an expansion vessel, which water is thentorn into droplets through the expanding air.

By alternately filling two ejecting receptacles, one obtains continuousoperation on the water-jet pump since a driving-out, or discharging,operation can be followed directly by a further driving-out operation,without need to pause for filling of the ejection chamber with water.

The arrangement of the ejecting receptacle and of the expansion vesselin an outer container has the advantage that pipelines are hardlyneeded, since the ejecting receptacles can be filled directly from theouter container. By using check valves, in particular valve caps, thestatic pressure in the outer container effects a filling of the ejectingreceptacles by which special filling means for filling the ejectingreceptacles are avoided. A particularly simple means for the alternateconnection of the ejecting receptacles to the water-jet pump employs aslide valve driven by the water leaving the ejecting receptacles. If oneof the ejecting vessels has become pressureless, the piston of the slidevalve is moved quickly by the pressure in the other receptacle, so thatthe emptied receptacle is closed off and now the receptacle which isunder pressure is connected to the water-jet pump.

For reasons of simplicity, reference is here made to one water-jet pump,even though of course several water-jet pumps can be connected to theapparatus. Favorable size relationships for the apparatus are achievedif it is designed for the operation of two to four water-jet pumps.

The arrangement of standpipes and compressed air supply hereafterdescribed assure water discharge without the danger of drivingcompressed air also flowing to the water-jet pump. However, one couldalso choose the arrangement differently. It is also not impossible topermit the driving compressed air to exit below the water level.

A reversing mechanism permits, with the simplest means, an automaticcontinuous operation of the apparatus such that the water-jet pump issupplied uninterruptedly with operating water.

The control of the compressed air by means of rotary slide valves can bedone simply. However, other advantages are also to be considered.Particularly simple becomes the construction, when one single rotaryslide valve controls both the supply of compressed air to the ejectingreceptacles and also the transfer of air from the ejecting receptaclesinto the expansion vessel. To drive the rotary slide valve it ispossible to use the above-mentioned reversing piston.

A particularly advantageous type of construction is obtained if onecombines the compressed air lines and valves and water channels in acontrol plate, which is utilized at the same time for holding theejecting receptacles and expansion vessel in the outer container.

It is also advantageous to arrange a water-jet pump or several water-jetpumps on the wall of the outer container, because through this pipelinesfor returning the operating water are eliminated. However, one also canarrange the water-jet pump at a different place and return the waterthrough lines, for example hoses.

The alternate filling and emptying of the ejecting receptacles can becontrolled also with a time-dependent control, through which after apregiven, preferably adjustable time interval a switching over from onedriving-out vessel to the other one takes place, whereby the timeinterval is chosen such that the switching over takes place for sureprior to the ejecting receptacle, which is emptying, becoming totallyempty.

If one brings the expanding air directly into contact with the water,one can advantageously arrange the expansion vessel above the water filland discharge the water and the expanded air at the lowermost point ofthe expansion vessel to assure in a simple manner the avoiding of anaccumulation of water in the expansion vessel.

If one introduces water at a right angle to the expanding compressedair, one achieves a particularly intensive and thus effective contactbetween the air, which is cooling off, and the water. The air flowthereby tears the water into small droplets. Atomization of the water isalso already effected by spraying it into the expansion vessel, wherebyalso its impact on solid surfaces assists its separation into smalldroplets. The cooling effect in the expansion vessel can be improvedsubstantially if one builds in baffle plates. Furthermore, one achieveswith such baffle plates a sound muffling.

BRIEF DESCRIPTION OF THE DRAWINGS

One exemplary embodiment of the invention is schematically illustratedin the drawings, in which:

FIG. 1 is a top view of an inventive apparatus,

FIG. 2 is a cross-sectional view along the line II--II of FIG. 1,wherein also a control slide valve for compressed air is cut,

FIG. 3 is a cross-sectional view along the line III--III of FIG. 1,wherein the cross-section plane also intersects the reversing mechanismfor the reversal of the compressed air flow,

FIG. 4 is a cross-sectional view along the line IV--IV of FIG. 1,wherein also the reversing mechanism for the water flow is included inthe cross section,

FIG. 5 is a horizontal cross-sectional view along the line V--V of FIG.2, wherein air channels for supplying of compressed air to ejectingreceptacles are included in the cross section,

FIG. 6 is a cross-sectional view along the line VI--VI of FIG. 2,wherein the channels for supplying of compressed air from the ejectingreceptacles to the let-down vessel are included in the cross section,

FIG. 7 is a cross-sectional view along the line VII--VII of FIG. 2,

FIG. 8 is a view which corresponds with FIG. 1, but of a modifiedembodiment in which the let-down vessel is arranged above the waterfilling, and

FIG. 9 is a view which corresponds to FIG. 4, but of the embodimentaccording to FIG. 8.

DETAILED DESCRIPTION

The main parts of the apparatus are an outer container 1, two ejectingreceptacles 2 and 3, a let-down (i.e. expansion) vessel 4, a compressedair control slide valve 5 with an associated reversing mechanism, whichas a whole is identified with reference numeral 6, a reversing piston 7for reversing the water flow and two water-jet pumps 8 and 9. Said mainparts, and further parts, and the cooperation of the parts of theapparatus will be discussed in detail hereinafter.

The outer container 1 has, as is shown in FIG. 1, a rectangular top viewand a relatively high height (see FIG. 2) compared with its top view.The outer container can for example be of plastic. Ledges 10, 11 and 12are built into the box bottom, onto which ledges the receptacles 2, 3and 4 are mounted, so that said receptacles are spaced from the bottom13 of the container 1. As is illustrated in FIG. 3, a water-dischargeopening 14 is arranged near the bottom 13, which opening is closed offby means of a plug 15.

The ejecting receptacles 2 and 3 have a cylindrical shape and are closedoff on top by a lid 16 and on the bottom by a screwed-on bottom 17. Bothreceptacles are constructed alike and are discussed in connection withthe example of the receptacle 2.

A large opening 18 exists in the bottom 17, which opening is closed offby a valve cap 19. The valve cap is pivotal about a horizontal axis 20and has a packing coating 21. A small edge 22 which surrounds theopening 18 serves as a packing seat for the valve cap.

A float 23 is arranged in each of the receptacles 2 and 3, which floatis vertically movable in a cage 24. The cage 24 has holes 24a, so thatits inside communicates with the inside 25 of the ejecting cylinder. Aconical valve 26 is provided on the upper side of the float 23, whichconical valve cooperates with a valve seat 27, which is provided on thelower end of the control pipeline 28, which is guided through the lid 16into the inside 25 of the ejecting receptacle.

The let-down vessel 4 is of a good heat-conducting material, for exampleof a rust-free steel, and carries ribs 4a on its outside. Baffle platesare arranged inside of the let-down vessel, which plates are for examplecross plates 29 and 30, which force air entering the let-down vessel todetour, so that a sound-muffling effect will occur.

An exhaust pipe 31 which projects upwardly is provided on the ceiling ofthe let-down vessel 4. The air which is supposed to be expanded isforced through the built-in baffle plates to flow through the let-downvessel first downwardly and then upwardly.

The receptacles 2, 3 and 4 are held in the container by a control platewhich as a whole is identified with reference numeral 32. Said controlplate lies on the upper sides of the receptacles 2, 3 and 4 and issecured against a lifting upwardly by means of holding elements 33 and34. Various openings are provided in said control plate. Furthermore thealready mentioned rotary slide valve 5 is supported in the controlplate. Furthermore the control plate receives the reversing piston 7, asis shown in the cross section of FIG. 4.

The rotary slide valve 5 has a cylindrical member, in which are providedtwo angular channels 35 and 36 (FIGS. 5 and 6) axially spaced from oneanother. At the height of the angular channel 35 (FIG. 5) three channels37, 38 and 39 are arranged in the control plate 32. The channel 38 has avertical section 38a, which leads to a compressed air connection 40(FIG. 1). The channel 37 leads from the opening 41, in which the rotaryslide valve 5 is supported, through a vertical section 37a into theejecting receptacle 2. The channel 39 lies symmetrically to the channel37 and leads into the ejecting receptacle 3.

In the position according to FIG. 5, the compressed air connection 40communicates with the ejecting receptacle 3. After a rotation of therotary slide valve 5 in clockwise direction at 90°, the ejectingreceptacle 2 is connected to the compressed air connection 40.

In the plane of the angular opening 36 (FIG. 6) there are provided inthe control plate three channels 42, 43 and 44. In the position which isillustrated in FIG. 6, the ejecting receptacle 2 is connected through avertical section 42a of the opening 42, the angular opening 36 in therotary slide valve 5 and the opening 44, which also has a verticalsection 44a, to the let-down vessel 4. After a rotation of the rotaryslide valve at 90°, the ejecting receptacle 2 is uncoupled from thelet-down vessel 4 and instead the ejecting receptacle 3 is coupled tothe let-down vessel 4.

As one can see from FIG. 2, the openings 37, 39, 42 and 43 lie in thesame vertical plane, so that also the mentioned vertical channelsections are in alignment. Said vertical channel sections are alignedwith openings 45 in the end surfaces 16 of the ejecting receptacles.Valve balls 46 are provided below said openings, which balls consist ofa material which is specifically lighter than water and which are eachguided in a cage 47, which has cross bores 47a.

Standpipes 48 and 49 are arranged in the ejecting receptacles 2 and 3(see FIG. 4). Said standpipes extend to the bottoms 17 and have slopedareas 48a at their ends. The standpipes 48 and 49 extend fixedly throughthe lids 16 of the ejecting receptacles and communicate with angularchannels 50 and 51 in the control plate 32. The angular channels endaxially in a cylinder 52, in which the piston 7 is movable. Valve seats53 and 54 are provided on the ends of the cylinder 52. The piston 7,which acts at the same time as a valve disk, has packing edges 7a, 7bwhich can rest against the valve seats 53 and 54. An opening 55 radiallyends in the longitudinal center of the cylinder 52, which opening 55(see FIG. 1) extends to the edge of the control plate 32. A pipeline 56is connected to the opening 55, which pipeline branches at its end intotwo pipelines 57 and 58, in which manual valves, or faucets, 59 and 60are provided. The pipelines 57, 58 lead to the water-jet pumps 8 and 9,on which suction connections 8a and 9a are provided, to which thereceptacles which are to be evacuated are connected, for example throughflexible hoses (not shown).

Two cylinders 61 and 62 (FIG. 3) are mounted on the control plate 32.The above-mentioned compressed air lines 28 end in communication withthe ends of the cylinder bores 61a and 62a. A rod 63 extends between thetwo cylinders 61 and 62, the ends of which are constructed as pistons 64and 65, which are fitted into the cylinder bores 61a and 62a. A recess66 is provided in the center of the rod, into which (see FIG. 1) engagesan arm 67, which is connected fixedly to the rotary slide valve 5 andprojects radially from the arm.

The apparatus operates as follows:

During the start of the operation, water is first added to fill theouter container 1 up to the level mark 68 (FIG. 3). The connection port40 for the compressed air supply is, as schematically shown in FIG. 1,connected to a compressed air line C, in which a manual valve V isprovided in front of said connection port and initially remains closed.Receptacles R which are to be evacuated are connected to the water-jetpumps 8 and 9 through the connections 8a and 9a. If at least one of themanual valves 59 and 60 is opened, the device starts to operate, whenthe compressed air valve in front of the connection 40 is opened.

During filling of the outer container 1 with water, the ejectingreceptacles 2 and 3 are also filled with water, whereby the valve caps19 are opened by the static pressure of the water. If the connection tothe let-down vessel 4 is opened, which is true for the ejectingreceptacle 2, in the valve position shown in FIG. 6, the air containedin the ejecting receptacle can escape and it can fill up completely.Penetration of water into the air channels 37 and 39 is prevented by thevalves 46, which through their buoyancy in the water are lifted andpressed against the opening in the cylinder lid 16. The other ejectingreceptacle from which the air discharge is not possible, will not beable to fill up completely, since an air cushion remains in said vessel.

It is assumed that (in contrast to the showing in FIG. 5) the positionof valve 5 is such that the compressed air flows into the ejectingreceptacle 2. The compressed air presses against the liquid surface andmoves the water through the standpipe 48 (see FIG. 4) upwardly. Thewater pressure presses the piston 7 against the valve seat 54 on theright and thus closes off the standpipe 49 of the other ejectingreceptacle 3. The water flows through the opening 55 to the water-jetpumps 8 and 9. The water which is emitted by the water-jet pumps fallsdirectly again into the outer container 1.

When the water level in the ejecting receptacle 2 has dropped so farthat the float 23 (see FIG. 3) can sink, the lower end of the controlline 28 opens and the compressed air, which is for example at an excesspressure of two atmospheres, can flow to the cylinder 61, which causesthe rod 63 to be pushed to the right. This rotates the rotary slidevalve 5 through 90°, to establish its connections shown in FIGS. 5 and6. In this position the compressed air flows through the connectionpiece 40 into the ejecting receptacle 3 and presses against the watersurface therein. The water is moved upwardly in the standpipe 49 andfirst drives the reversing piston 7 to the left, whereby the packingedge 7a is set on the seat 53 and thus closes off the standpipe 48. Inthis position, water is moved from the ejecting receptacle 3 through theopening 55 to the water-jet pumps.

At the same time, as is illustrated in FIG. 6, a connection opensbetween the ejecting receptacle 2 and the let-down vessel 4 through thechannels 42, 36 and 44. The compressed air, which at the moment of thechanging over is still under its full pressure of two atmospheres excesspressure (a releasing of the compressed air does not take place duringejection), now expands into the let-down vessel 4, whereby a strongcooling of the air occurs. At the same time, air noise is reducedthrough the sound-muffling effect of the let-down vessel 4. The cold airabsorbs heat from the water which washes totally around the receptacle4, which causes the water to be kept at a low temperature. The expandedair is discharged through the pipe 31.

If in the ejecting receptacle 3 the water level has dropped so far thatthe float 23 therein drops, the cylinder 62 is placed under pressure andthe rod 63 is pushed to the left, after which again exists the situationat the beginning of the above-described operating sequence. Thus, whilewater is driven out of an ejecting receptacle with the help ofcompressed air, the other ejecting receptacle is filled through itsbottom 17 due to the static pressure which exists in the outercontainer 1. The supply openings 18 are chosen large, in order to assurea complete filling of the emptied ejecting receptacle at the relativelylow static pressure, prior to emptying of the ejecting receptacle whichunder pressure is being emptied.

It is sufficient for short interruptions in the operation to shut offthe faucets 59 and 60. It is advantageous during a longer pause in theoperation to also shut off the compressed air supply to connection 40.

To empty the device, the water-discharge screw 15 is loosened duringoperation. The ejecting receptacles 2 and 3 are then pumped emptyautomatically. A continuous water change is not needed, since the wateris being cooled at all times. Because of unavoidable contaminations, itis advantageous to change one time per day the water fill, which can befor example approximately 25 liters.

In the embodiment according to FIGS. 8 and 9, the let-down vessel, whichis here identified as a whole by reference numeral 70, is arrangedhorizontally above the water level. The let-down vessel 70 is acylindrical container, which can be of a metal. Perforated sheet metalplates 71 are arranged in said vessel 70, of which plates some areillustrated in FIG. 9.

A water line 72 is connected to the end of the vessel 70, which end ison the right in the drawing. The water line 72 branches off frompressure line 56 which leads to the water-jet pumps. The water line 72ends by means of a nozzle 73 in the vessel 70. The jet direction of thenozzle 73 is directed at a right angle to the longitudinal direction ofthe vessel 70 and downwardly.

The air which exits from the ejecting receptacles 2, 3 is introducedinto the vessel 70 through a line 74. The line 74 has an outlet opening74a, the axis of which extends parallel to the longitudinal direction ofthe vessel 70 and is arranged below the water-supply nozzle 73, but islaterally offset slightly to the right from same.

The device according to FIGS. 8 and 9 operates substantially in the samemanner as the device according to FIGS. 1 to 7. The main difference isthat water is introduced into the let-down vessel 70. The water isdivided finely during spraying in under pressure, through tearing apartof the jet and through the impact onto the baffle plates 71. A furtherdivision and distribution in the entire let-down vessel is effected bythe air blasts which exit from the air-line port 74a. The water isdistributed on the perforated sheet-metal plates 71, which thusgenerally are coated by a film of water. The water is ejected from thevessel 70 together with the air, through an exhaust line 75. The outlet75a of the exhaust line 75 ends above the water level 76 in thesurrounding area and is directed downwardly. Thus, in this embodimentthe water level lies slightly lower than in the embodiment of FIGS. 1 to7. A horizontal part 75b of the exhaust line 75 extends through the wallof the vessel 70 at the lowest point therein. This assures that no watercan accumulate in the vessel 70.

Although particular preferred embodiments of the invention have beendisclosed in detail for illustrative purposes, it will be recognizedthat variations or modifications of the disclosed apparatus, includingthe rearrangement of parts, lie within the scope of the presentinvention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method for theoperation of a water-jet pump, in which the water which is needed forthe operation of the pump is recirculated in a cycle, in which theimprovement comprises pressurizing the water by means of compressed airat a substantially constant air pressure, the compressed air driving thewater through the water-jet pump, and expanding the compressed air in adefined let-down space, wherein heat is withdrawn from the water, whichheat is absorbed by the air during and after its expansion.
 2. A methodaccording to claim 1, wherein the water flows around the definedlet-down space.
 3. A method according to claim 1, wherein the expandingair contacts the water directly.
 4. A method according to claim 3,wherein the air and water are both introduced into the defined let-downspace.
 5. A method according to claim 1, wherein at least two ejectingchambers are filled alternately with compressed air, wherein during thefilling of a said chamber with air, water therein is compressed anddriven from said chamber to said water-jet pump and wherein air which iscontained in the other ejecting chamber is expanded in the let-downspace.
 6. An apparatus for operating a water-jet pump, comprising atleast two ejecting receptacles, connection water channels which connectthe ejecting receptacles to the water-jet pump, at least one let-downvessel, first connection air channels which connect the ejectingreceptacles to the let-down vessel, a compressed air connection forsupplying compressed air, further connection air channels which connectthe compressed air connection to the ejecting receptacles, first watervalve means for effecting alternate fluid connection of the ejectingreceptacles to the water-jet pump through the connection water channels,second water valve means for effecting fluid connection of the ejectingreceptacles to the water which is discharged from the water-jet pump,first compressed air valve means for effecting alternate fluidconnection of the ejecting receptacles to the compressed air connectionthrough the further connection air channels and second compressed airvalve means for effecting alternate fluid connection of the ejectingreceptacles to the let-down vessel through the first connection airchannels.
 7. An apparatus according to claim 6, wherein the ejectingreceptacles and the let-down vessel are arranged in an outer container,which is taller than the ejecting receptacles and which can be filledwith water, and wherein the discharge side of the water-jet pump ends inthe outer container and the ejecting receptacles each have in the areaof their bottom a flow connection, which leads to the inside of theouter container and can be closed off by the second water valve means.8. An apparatus according to claim 7, wherein the second water valvemeans includes check valves.
 9. An apparatus according to claim 6,wherein the first water valve means is controlled by the water exitingfrom the ejecting receptacles.
 10. An apparatus according to claim 9,wherein said first water valve means includes a piston which slides in acylindrical chamber, the ends of the chamber being connected by firstportions of said connection water channels to the ejecting receptaclesand a portion of the chamber intermediate its ends being connected by afurther portion of said connection water channels to the water-jet pump,the piston in each end position closing off a respective one of thefirst channel portions but leaving the further channel portion in fluidconnection with the other first channel portion.
 11. An apparatusaccording to claim 6, wherein said connection water channels includestandpipes arranged in the ejecting receptacles, which standpipes endnear the bottom of the ejecting receptacles.
 12. An apparatus accordingto claim 6, wherein the further air connection channels for theintroduction of compressed air into the ejecting receptacles end in theupper area of the ejecting receptacles.
 13. An apparatus according toclaim 6, including reversing means responsive to the compressed air inthe ejecting receptacles for operating the first and second compressedair valve means after one said ejecting receptacle is filled with air toconnect the compressed air connection to the other said ejectingreceptacle and said one ejecting receptacle to the let-down vessel. 14.An apparatus according to claim 13, including near the bottom of eachejecting receptacle a float valve which closes off an air channel whenits floating member is submerged into the water, which air channel leadsto said reversing means.
 15. An apparatus according to claim 6, whereinthe first and second compressed air valve means respectively includefirst and second compressed air valves which are constructed as rotaryslide valves.
 16. An apparatus according to claim 15, wherein the firstand second compressed air valves are provided in a single rotary slidevalve member which is rotatably supported in a housing, wherein thesingle rotary slide valve member has, in a first plane, openings for thefirst compressed air valve and, in a second plane which is provided atan axial distance from the first plane, further openings for the secondcompressed air valve, said openings cooperating with additional openingswhich are arranged in spaced planes in the rotary slide valve housing.17. An apparatus according to claim 16, including reversing meansresponsive to air pressure in the ejecting receptacles for effectingrotational movement of the rotary slide valve member.
 18. An apparatusaccording to claim 17, including a radially projecting pin on the rotaryslide valve member, which pin is operatively engaged by the reversingmeans.
 19. An apparatus according to claim 6, including a control platewhich rests on the ejecting receptacles and the let-down vessel and issecured against lifting off in an upward direction, and which containsthe first and second compressed air valve means and at least a portionof the first and second compressed air connection channels.
 20. Anapparatus according to claim 7, wherein the water-jet pump is arrangedon a wall of the outer container and discharges directly into the outercontainer.
 21. An apparatus according to claim 7, wherein the let-downvessel is arranged above the water fill level of the outer container, isconnected by at least one water channel to at least one ejectingreceptacle and has an outlet opening at its lowest point for thedischarge of a water/air mixture.
 22. An apparatus according to claim21, wherein the outlet opening for the discharge of the water/airmixture from the let-down vessel lies above the water level in the outercontainer.
 23. An apparatus according to claim 21, wherein for theintroduction of the water into the let-down vessel there is provided anozzle, the jet direction of which is oriented at an angle to the axisof the opening into the let-down vessel for the first air connectionchannels.
 24. An apparatus according to claim 6, wherein the let-downvessel contains baffle plates.